Constant velocity joint of tripod type

ABSTRACT

A constant velocity joint comprises: a hollow housing having a plurality of guide grooves; a tripod having a plurality of trunnions positioned in the guide grooves; and a roller assembly disposed on each trunnion. The outer roller includes a convex outer surface, the convex outer surface having a first radius (Rry) seen from a cross section taken in an orthogonal direction of the outer roller, the convex outer surface having a second radius (Rrx) seen from a cross section taken along the central axis of the outer roller, in which the center of the second radius (Rrx) is displaced outwardly from the center of the first radius (Rry), and the second radius (Rrx) is shorter than the first radius (Rry).

REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application No. 12/139,427 filed onJun. 13, 2008, now U.S. Pat. No. 8,177,649, the entire contents of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a constant velocity joint of tripodtype, which is disposed between a drive shaft and a driven shaft coupledto each other and typically used in a drive axle of, for example, anautomobile for transmitting rotational torque between the rotatingshafts.

BACKGROUND OF THE INVENTION

Tripod type constant velocity joints are well known in the automobileindustry as one type of constant velocity joints used in the drivesystem of automobiles to transfer a uniform torque and a constant speed,while operating with a wide range of joint angle.

For instance, one example of the tripod type constant velocity joint wasillustrated in Japanese Patent Application, S62-233522. This tripod typeconstant velocity joint typically includes tripod fixed to an end of thesecond rotating shaft, which functions as a driven member, and hollowcylindrical housing fixed to an end of the first rotating shaft whichfunctions as a drive member. Three circumferential grooves are formed atthree locations on the inner face of the housing at equal spacing in thecircumferential direction and extend in the shaft direction of thehousing. Each tripod comprises a boss connected to the second rotatingshaft, and each trunnion has a cylindrical shape and extends radiallyfrom three locations at equal spacing around the boss. Each trunnion hasa roller fixed at a distal end of the trunnion and with needle rollersengaged therein. In this arrangement, each roller can freely rotateabout the trunnion while also be displaced in the axial direction of thetrunnion. The constant velocity movement between the first and secondrotating shafts is ensured with the rollers rotatably and displaceablyengaging in the grooves disposed along the inner face of the housing. Inorder to facilitate the sliding movement, a pair of side faces areformed in circular recesses on each side of the respective grooves, andeach roller is supported rotatably and pivotally along the side faces ofthe grooves.

When the first and second rotating shafts rotate with a joint anglepresent between the first and second shafts, each roller moves withcomplexity. For example, each roller moves in the axial direction of thehousing along each of the side faces of the respective guide grooves,while the rollers change in orientation and further displace in theaxial direction of the trunnion. Such movement of the rollers cannotcause a relative movement between a peripheral outside face of each ofthe rollers and each of the side faces to be smoothly made. Thus, arelatively large friction occurs between the faces. As a result, thistripod type constant velocity joint produces three-directional axialforces as the shafts rotate. In the application of a prior art tripodjoint to the vehicles, it is known that the axial forces may cause atransverse vibration typically referred to as “shudder”. This shudderdisturbance may become severe particularly when a large torque istransmitted with a relatively large joint angle present.

In order to restrain or reduce such conventional shudder phenomena,various suggestions have been introduced. Among various attempts, theinventors of this application have particularly discovered that theconventional shudder problem can be reduced by providing sufficientlubrication channels in the contact surfaces between the convex outersurface of the roller and the corresponding inner surface of respectiveguide grooves of the housing and also by optimally controlling thedistribution of the contact force and/or the contact angle between theroller and the corresponding contact groove of the housing.

FIG. 1 illustrates an example of a conventional constant velocity joint,which includes a housing 12 of an outer joint member (i.e., a drivingmember), and three radially-projecting trunnions 16 of an inner jointmember (i.e., a driven member) internally coupled within respectiveguide groove of the housing 12. Each trunnion 16 is received within aroller assembly which is composed of outer roller 13, inner roller 14,and multiple needle bearings 15 engaged between the outer and innerrollers 13 and 14. As shown, the guide groove has a circularcross-sectional shape with a surface radius Rg, and the outer surface ofthe outer roller 13 similarly has a circular cross-sectional shape witha surface radius Rrx (in the cross section taken along the axis of thetrunnion 16 or the outer roller 13, as shown in the upper drawing ofFIG. 1). The radius Rrx of the outer roller 13 is a little smaller thanthe radius Rg of the housing 12, thus leaving a clearance “S”there-between, which is necessary in order to manufacture and assemblethe apparatus. In addition, lubricants (e.g., grease) can be filled inthis clearance “S” for lubrication and to reduce frictions in thecontact areas. As shown in the lower drawing of FIG. 1, the outer roller13 further includes another circular cross-sectional shape with asurface radius Rry (in the cross section taken in orthogonal directionrelative to the axis of the trunnion 16 or the outer roller 13).

In operation, the trunnion 16 can be displaced radially and pivotallyrelative to the guide groove of the housing 12, and this movement of thetrunnion 16 associated with the resultant friction with the rollerassembly causes the outer roller 13 to move reciprocally in an axialdirection (e.g., in the Y-axis direction in FIG. 1), in part, due to thepresence of clearance “S”.

As illustrated in FIG. 2, when the outer roller 13 moves upwardly in thegroove of the housing 13, the outer roller 13 contacts with the housingat “P1” on an upper portion of the housing groove with axialdisplacement δ and contact angle β defined therein. This causes theclearance S1 at upper portion 121 c of the housing groove to besubstantially narrowed while enlarging the clearance S2 at lower portion122 c of the housing groove. As a result, the grease filled in the upperclearance S1 squeezes out from the clearance and the contact frictionincreases substantially, and thus, causing to generate adversevibrations or disturbance to the vehicle. As illustrated in FIG. 3, whenthe outer roller 13 moves downwardly in the groove of the housing 13,the outer roller 13 contacts with the housing at “P2” on a lower portionof the housing groove with its axial displacement δ and contact angle βdefined thereby. This causes the clearance S2 at the lower portion ofthe housing groove to be substantially narrowed while enlarging theclearance S1 at the upper portion of the housing groove. As a result,the grease filled in the lower clearance S2 squeezes out from theclearance and the contact friction increases substantially, and thus,causing to generate adverse vibrations or disturbance to the vehicle. Inthe drawing, the undefined reference “O” is the center of the opposinghousing grooves, and reference “Or” is the center of the displaced outerroller 13.

SUMMARY OF THE INVENTION

In order to solve the above described and other problems or drawbacksknown in the conventional constant velocity joints, the presentinvention provides a tripod type constant velocity joint with a reliableand compact structure which can also reduce the conventional shudderphenomena, preferably, by providing effective lubricant channels andalso by optimally controlling the distribution of the contact forceand/or the contact angle between the roller and the correspondingcontact groove of the housing.

In order to provide more spacious lubricant channels for reducing thefrictional force in the contact areas, it would be better to reduce boththe elliptical contact area (such as the cross hatched region in FIG. 4)and the contact angle β1 (FIG. 4). According to Hertzian theory, thecontact area between the parts under load is determined by the amount ofthe load, the mechanical strength (e.g., elastic deformationcoefficients) of the parts, and surface curvature of the contact area.Thus, if the contact area is reduced excessively, the mechanicalstrength and durability of the assembly will be deteriorated due to theincrease in the surface contact stress of the parts. On the other hand,due to the design limitations it is more difficult to adjust the contactangle rather than to reduce the elliptical contact area. This is becausethe contact angle β1 under a load is primarily determined by the rollingfriction coefficient μ (as the contact angle is a function of thefriction coefficient, namely, β1=a tan(2μ/cosθ)) except when the rollerassembly is guided in the housing groove with the outer roller tiltedand guided in the track of the housing in Z direction during therotation of the joint. Thus, substantial considerations are made in thepresent invention to determine the curvature of the housing groove andits corresponding outer surface of the outer roller, and the contactarea and the contact angle are optimized.

The applicant (namely, the inventor) of present invention hasdiscovered, among others, the following two solutions to reduce theelliptical contact areas for the purposes of providing more greasechannels in the contact areas of the constant velocity joints andreducing the frictions there-between. One is by changing the curvaturesof the housing groove and its corresponding outer roller. The other isby reducing a load applying on the housing groove, preferably bydistributing a concentrated load to two or more distributed loads. Inconventional tripod joints as shown in FIG. 1, the surface curvature orradius (Rrx) of the outer roller 13 seen from the cross section takenalong the axis of the trunnion 16 or the outer roller 13 is identical tothe surface curvature or radius (Rry) of the outer roller 13 seen fromthe cross section taken in orthogonal direction relative to the axis ofthe trunnion 16 or the outer roller 13. In this joint, as shown in FIG.1, the inner surface radius (Rg) of the housing groove, seen from thecross section taken in orthogonal direction relative to the axis of thehousing groove, is approximately as same as, but a little larger than,the surface radius Rrx of the outer roller 13 by the clearance margin of“S”.

The present applicant has also discovered that the elliptical contactareas can be reduced by having the radii Rrx and Rg shortened whilemaintaining the radius Rry the same, for example, as illustrated inFIGS. 4-6 of the present invention. In FIGS. 4-6, seen from the crosssection taken in orthogonal direction relative to the axis of thehousing groove, the center “O1” of both the radial inner surface of thehousing groove (having the radius Rg) and the radial outer surface ofthe outer roller 13 (having the radius Rrx) are displaced outwardly fromthe center “O” of the radial outer surface of the outer roller 13(having the radius Rry) seen from the cross section taken in orthogonaldirection relative to the axis of the trunnion 16 or the outer roller13. This modified configuration of the invention can facilitate thereduction of the frictional force in the contact areas.

The present invention further provides an enlarged grease space in thecontact areas between the housing groove and its corresponding outerroller to effectively fill the lubricant grease for reducing thefrictions there-between. This can be realized by modifying the innertrack or groove structure of the housing. In one preferred embodiment asillustrated in FIG. 4 and FIG. 5, the inner track structure of thehousing is modified to provide an upper side recess area S1 and a lowerside recess area S2, and thus, defining widened spaces between the guidegroove of the housing and its corresponding upper and lower portions ofthe convex outer roller as shown. In another preferred embodiment asillustrated in FIG. 5, the inner track structure of the housing isfurther modified to provide an inner recess area S3, and thus, defininga widened space between the guide groove of the housing and itscorresponding portion of the convex outer roller for filling more greasein the recess area. This modified structure further facilitatesdistribution of a concentrated load to multiple distributing loads atupper and lower sides of the outer roller, and thus, enabling a furtherreduction of the frictional forces in the contact area.

According to the embodiments shown in FIGS. 4 and 5, the size L of thecylindrical or concave groove area of the housing groove is preferablydetermined to cover the elliptical contact areas (e.g., thecross-hatched area in FIG. 4) in the upper and lower sides of thehousing groove. Thus, the inner starting points of the upper recess areaS1 and the lower recess area S2 are determined to be coincident with, orlocated a little (preferably, up to 12 mm) outside from, the outermostpoints of the elliptical contact areas. The concave groove size L ispreferably in a range determined by the equation of: L/Rry=0.25-0.6.

In the embodiment as shown in FIG. 5, the size L1 of the upper and lowerconcave (e.g., cylindrical) groove portions is respectively selected tohave a dimension the same or a little (preferably, up to 4 mm) largerthan the dimension “a” of the elliptical contact area. As a result, thesize of inner recess S3 is also determined accordingly.

According to another preferred embodiment as illustrated in FIG. 6, theinner track structure of the housing is modified to provide an upperrecess area S1′, a lower recess area S2′, and an inner recess area S3′for filling more grease in the recess area. This modified structurefurther facilitates distribution of a load to multiple (e.g., two)distributing loads at upper and lower sides of the outer roller, andthus, enabling a further reduction of the frictional forces in thecontact area. In this embodiment, the inner surface of the housinggroove is particularly configured to have a first elliptical surface inthe upper half of the inner housing groove and a second ellipticalsurface in the lower half of the inner housing groove, in which thecenter “Or” of the two ellipses is coincident at the same location andis displaced outward to a distance from the center “O” of the outerroller. The two ellipses of the housing groove respectively have alonger diameter AA and a shorter diameter BB. The ratio BB/AA of the twodiameters is preferably between 0.65 and 0.95, and the ratio AA/2Rrx ispreferably between 1.1 and 1.4. In this embodiment, the size L2 (that isthe distance between two contact points P1 and P2 where the outer rollercontacts with the housing groove composed of two elliptical surfaces) ispreferably selected to have a dimension in a range between 0.60 BB and0.85 BB where BB refers to the shorter diameter of the two ellipses.

In this embodiment, due to the curvature difference of between thecircular outer surface of the outer roller and the elliptical contour ofthe housing groove, the elliptical contact areas can be reduced thanthat of the conventional one (as shown in FIG. 1) in which the outersurface of the outer roller and the inner surface of the housing groovehave concentric circular shapes. However, it is noted that the reductionof the elliptical contact area is to be limited to a suitable degree inconsideration of the required mechanical strength of the outer rollerand the housing. Thus, the curvatures of the roller and the housinggroove should be determined based on the design requirements of theconstant velocity joint.

According to one preferred embodiment of the present invention, aconstant velocity joint for a drive system (having a first rotatingshaft and a second rotating shaft coupled with the constant velocityjoint) comprises: a hollow housing having a plurality of guide groovestherein, the guide grooves extending in an axial direction of thehousing and spaced equally apart in a circumferential direction of thehousing; a tripod having a plurality of trunnions, each trunnionpositioned in a corresponding one of the guide grooves of the hollowhousing; and a roller assembly disposed on each trunnion, the rollerassembly including an outer roller for rollably receiving in thecorresponding guide groove. The outer roller includes a convex outersurface, the convex outer surface having a first radius (Rry) seen froma cross section taken in an orthogonal direction relative to a centralaxis of the outer roller, the convex outer surface having a secondradius (Rrx) seen from a cross section taken along the central axis ofthe outer roller, a center of the second radius (Rrx) displacedoutwardly from a center of the first radius (Rry), and the second radius(Rrx) being shorter than the first radius (Rry). Each of the guidegrooves of the housing includes a concave surface for mating with theconvex outer surface of the outer roller, the guide groove furtherincludes upper and lower recess areas respectively recessed from theconcave surface of the groove, and thereby defining widened spacesbetween the guide groove of the housing and its corresponding upper andlower portions of the convex outer roller.

The length (L) of the concave portion of the guide groove is preferablythe same as or a little longer than a distance covering elastic contactareas at the upper and lower portions of the outer roller. The length(L) of the concave portion of the guide groove is preferably in a rangeselected from an equation of: L/Rry=0.25-0.6.

According to another preferred embodiment of the invention, the guidegroove further includes an inner recess area recessed from an inner orcentral area in the concave surface of the groove for defining a widenedspace between the guide groove of the housing and its correspondingportion of the convex outer roller.

According to another preferred embodiment of the present invention, theconstant velocity joint for a drive system comprises: a hollow housinghaving a plurality of guide grooves therein, the guide grooves extendingin an axial direction of the housing and spaced equally apart in acircumferential direction of the housing; a tripod having a plurality oftrunnions, each trunnion positioned in a corresponding one of the guidegrooves of the hollow housing; and, a roller assembly disposed on eachtrunnion, the roller assembly including an outer roller for rollablyreceiving in the corresponding guide groove. The outer roller includes aconvex outer surface, the convex outer surface having a first radius(Rry) seen from a cross section taken in an orthogonal directionrelative to a central axis of the outer roller, the convex outer surfacehaving a second radius (Rrx) seen from a cross section taken along thecentral axis of the outer roller, a center of the second radius (Rrx)displaced outwardly from a center of the first radius (Rry), and thesecond radius (Rrx) being shorter than the first radius (Rry). Eachguide groove of the housing is formed with a first elliptical surface inan upper half of the housing groove and a second elliptical surface in alower half of the housing groove, the center of the first and secondelliptical surface is located at the same location with or in proximityof the center of the second radius (Rrx) of the outer roller.

The first and second ellipse shapes of the housing groove are preferablyformed of the same ellipse with a longer diameter (AA) and a shorterdiameter (BB). The ratio BB/AA of the two diameters is preferablybetween 0.65 and 0.95, and ratio AA/2Rrx is preferably between 1.1 and1.4. The distance (L2) between two contact points where the outer rollerregularly contacts with the housing groove composed of the twoelliptical surfaces is selected to have a dimension in a preferablerange between 0.60 BB and 0.85 BB. The ratio BB/AA and a size of elasticcontact areas of between the outer roller and the housing groove areselected, preferably, in further consideration of mechanical strengthrequirements of the outer roller and the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described and other objects, features and advantages of thepresent invention will be more apparent from the presently preferredembodiments of the invention disclosed in the following description andillustrated in the accompanying drawings, in which:

FIG. 1 shows partial cross-sectional views illustrating an exemplaryconstruction of a conventional tripod type constant velocity joint;

FIG. 2 shows a partial cross-sectional view of the conventional tripodtype constant velocity joint as shown in FIG. 1, in which the outerroller is displaced upwardly relative to the outer housing of theconstant velocity joint;

FIG. 3 shows a view similar to FIG. 2, in which the outer roller isdisplaced downwardly relative to the outer housing of the constantvelocity joint;

FIG. 4 is a partial cross-sectional view of a tripod type constantvelocity joint, constructed according to one preferred embodiment of thepresent invention;

FIG. 5 is a partial cross-sectional view of a tripod type constantvelocity joint, constructed according to another preferred embodiment ofthe present invention; and

FIG. 6 is a partial cross-sectional view of a tripod type constantvelocity joint, constructed according to another preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 4-6 of the drawings, the tripod type constantvelocity joints of the present invention are described herein in detailswith several exemplary or preferred embodiments thereof. However, thefollowing descriptions of such embodiments are intended primarily forillustrating the principles and exemplary constructions of the constantvelocity joints of the present invention, and the present invention isnot specifically limited to these exemplary embodiments. Thus, oneskilled in the art can appreciate or recognize that variousmodifications and substitutions can be made thereto without departingfrom the spirit and scope of the present invention.

Common elements and general constructions of the constant velocityjoints of the type to which the present invention is related are knownin the art and described, for example, in the present applicant's priorapplications Ser. No. 11/750,138 (which is now U.S. Pat. No. 7,819,752),Ser. No. 11/840,194 (which is now U.S. Pat. No. 7,878,914), and Ser. No.11/947,307, and the entire contents of which are incorporated herein byreference. Accordingly, detailed descriptions of the constant velocityjoints are not repeated herein for simplicity purposes.

With reference to FIG. 4, one preferred embodiment of the presentinvention is described below with further details. In this embodiment,in order to provide more grease channels in the contact areas of theconstant velocity joints than that of the conventional joints as shownin FIG. 1, the center “O1” of both the radial inner surface of thehousing groove and the radial outer surface of the outer roller 303(both surfaces seen from the cross section taken in orthogonal directionrelative to the axis of the housing groove) is displaced outwardly fromthe center “O” of the radial outer surface of the outer roller 303(having the radius Rry) which surface is seen from the cross sectiontaken in orthogonal direction relative to the axis of the outer roller303. Accordingly, the curvatures or radius of the radial inner surfaceof the housing groove and the radial outer surface of the outer rollerare substantially reduced relative to the conventional joints as shownin FIG. 1. Thus, this modification leads to effectively reduce theelliptical contact areas between the outer roller and inner housinggroove, and results in the reduction of the adverse frictional force inthe contact areas as discussed above.

Moreover, having the center “O1” of the radial outer surface of theouter roller 303 displaced outwardly, the size of the outer roller 303can be reduced more compactly and the shape of the housing 302 can bemodified effectively, for example, to provide lateral recesses 302 a and302 b at the upper and lower sides of the housing groove whilemaintaining or otherwise reducing the size of the housing 302.

Referring still to FIG. 4, the contact angle β1 is typically determinedby the design requirements of the joints. Having the center “O1” of theradial outer surface of the outer roller 303 displaced outwardly fromthe center “O”, while maintaining the contact angle β1 the same, thecontact points of the outer roller 303 against the housing 302 movesinwardly from point B (which is equivalent to the contact point P1 ofthe conventional joint of FIG. 1) to point A. As a result, the thicknessof the outer roller 303 and the size of the housing groove (and thus, ofthe housing 302) can be reduced than that of the conventional joint, andaccordingly, the joint of the present invention can be made in a compactsize and reduced weight.

According to the present invention as illustrated in FIG. 4, the innerstructure of the housing is further modified to provide an upper siderecess area S1 and a lower side recess area S2, by removing the radialsurface portions in the upper and lower sides of the housing. Due tothese enlarged recess areas S1 and S2, lubricating grease can be moreeasily filled or introduced in the contact areas of the joints, and theadverse frictions can be limited.

In this embodiment, the size L of the concave housing groove ispreferably selected to cover the elliptical contact areas (thecross-hatched area in FIG. 4) in the upper and lower sides of thehousing groove. Thus, the inner starting points of the upper recess areaS1 and the lower recess area S2 are set to be the same location with, orlocated a little (preferably, up to 12 mm) outside from, the outermostpoints of the elliptical contact areas of the joints. The concave groovesize L is preferably in a range determined by the equation of:L/Rry=0.25-0.6.

With reference to FIG. 5, another preferred embodiment of the presentinvention is described below. This embodiment is similar to theembodiment of FIG. 4 described above, and the description of commonfeatures thereof are to be referred above and not repeated herein forsimplicity purposes. This embodiment, however, further includes anadditional recess area, namely the inner recess area S3, in addition tothe upper and lower recesses S1 and S2. Thus, this embodiment canreceive a further amount of grease in the three (or more) recess areas,and the contact frictions can be further limited.

In this embodiment, the overall length L of the concave housing grooveis determined in the same manner as that of the previous embodiment ofFIG. 4. Accordingly, the size L of the concaved (e.g., cylindrical)groove is set to cover the elliptical contact areas in the upper andlower sides of the housing groove. In addition, the concave groove sizeL is preferably in a range determined by the equation of:L/Rry=0.25-0.6. Moreover, the size L1 of each of the upper and lowerconcave groove portions is respectively selected to have a dimension thesame or a little (preferably, up to 4 mm) larger than the dimension “a”of the elliptical contact area. As a result, the size of inner recess S3is also determined accordingly.

With reference now to FIG. 6, another preferred embodiment of thepresent invention is described below. This embodiment is constructedwith similar basic concepts or principles as the above describedembodiments of FIGS. 5 and 6. However, the concave groove of the housing302″ (seen from the cross section taken in a perpendicular directionrelative to the longitudinal axis of the groove) is composed of twoelliptical surfaces, namely, a first elliptical surface (of contour E1)in the upper half of the inner housing groove and a second ellipticalsurface (of contour E2) in the lower half of the inner housing groove.Here, the center “Or” of the two ellipses is located at the samelocation with, or in proximity of, the center of the second radius (Rrx)of the outer roller, which location is displaced outwardly to apredetermined distance from the center “O” of the circular outer roller303 (seen from the cross-section taken in a perpendicular direction tothe axis of the outer roller). The two ellipses of the housing grooverespectively have a longer diameter AA and a shorter diameter BB. Theratio BB/AA of the two diameters is preferably between 0.65 and 0.95,and the ratio AA/2Rrx is preferably between 1.1 and 1.4.

As shown in FIG. 6 (seen from the cross-section taken along the axis ofthe outer roller), the outer surface of the outer roller 303 has acircular shape (with radius Rrx and center “Or”). Thus, as the circularouter roller 303 contacts with the two elliptical inner surfaces of thehousing, three recessed areas are formed between the two parts, namely,an upper recess area S1′ at the upper groove region 302 a″, a lowerrecess area S2′ at the lower groove region 302 b″, and an inner recessarea S3′ at the central groove region 302 c″. These recessed spaces aresuitable for retaining lubricant grease therein, and thus, thisembodiment is also effective in reducing the frictional contacts in thejoints.

In addition, this modified structure of FIG. 6 further facilitatesdistribution of a load to multiple (e.g., two) distributing loads atupper and lower sides of the outer roller, and thus, enabling a furtherreduction of the frictional forces in the contact areas. In thisembodiment, the size L2 (that is the distance between two contact pointsP1 and P2 where the outer roller contacts with the housing groovecomposed of two elliptical surfaces) is preferably selected to have adimension in a range between 0.60 BB and 0.85 BB where BB refers to theshorter diameter of the two ellipses.

In this embodiment, due to the curvature difference of between thecircular outer surface of the outer roller 303 and the two ellipticalcontour of the housing groove, the elliptical contact areas between theparts can be reduced than that of the conventional one (as shown inFIG. 1) in which the outer surface of the outer roller and the innersurface of the housing groove have concentric circular shapes (i.e.,same curvature). However, it is noted that the reduction of theelliptical contact area is to be limited to a suitable degree inconsideration of the required mechanical strength of the outer rollerand the housing. Thus, the curvatures of the roller and the housinggroove should be determined based on the design requirement of theconstant velocity joint.

As described above in connection with several exemplary embodimentsthereof, the contour and surface curvatures of the outer roller and theinner housing groove of the constant velocity joints are modified toreduce the contact or rolling frictions between the outer roller and thehousing. Moreover, the present invention provides ample and effectivegrease channels in the contact areas between the outer roller and thehousing groove for retaining greases therein, and thus, further reducingthe frictional contacts between the parts. Further, the presentinvention provides a suitable structure for distributing a concentratedload to two or more distributed loads along the inner surface of thehousing, and thus, enabling a further reduction of the frictional forcesin the contact areas of the joints.

The above disclosed embodiments of the invention are representatives ofa presently preferred form of the invention, but are intended to beillustrative rather than definitive thereof. Accordingly, those skilledin the art will appreciate or recognize that various modifications andsubstitutions can be made thereto without departing from the spirit andscope of the present invention as set forth in the appended claims.

What is claimed is:
 1. A constant velocity joint for a drive systemcomprising: a hollow housing having a plurality of guide groovestherein, the guide grooves extending in an axial direction of thehousing and spaced equally apart in a circumferential direction of thehousing; a tripod having a plurality of trunnions, each trunnionpositioned in a corresponding one of the guide grooves of the hollowhousing; and a roller assembly disposed on each trunnion, the rollerassembly including an outer roller for rollably receiving in thecorresponding guide groove; wherein the outer roller includes a convexouter surface, the convex outer surface having a first radius (Rry) seenfrom a cross section taken in an orthogonal direction relative to acentral axis of the outer roller, the convex outer surface having asecond radius (Rrx) seen from a cross section taken along the centralaxis of the outer roller, the convex outer surface of the second radius(Rrx) formed throughout an entire side surface of the outer roller, acenter of the second radius (Rrx) displaced outwardly from a center ofthe first radius (Rry), and the second radius (Rrx) being shorter thanthe first radius (Rry); wherein each of the guide grooves of the housingincludes a concave surface for mating with the convex outer surface ofthe outer roller, the concave surface having a length (L) and a radius(Rg) seen from a cross section taken along the central axis of thehousing, a center of the radius (Rg) being the same as the center of thesecond radius (Rrx) of the outer roller, and the second radius (Rrx) ofthe outer roller being shorter than the radius (Rg) of the housing by aclearance margin throughout an entire length (L) of the concave surface,wherein the guide groove further includes an upper recess area and alower recess area respectively recessed from the concave surface of thegroove, and thereby defining widened spaces between the guide groove ofthe housing and its corresponding upper and lower portions of the convexouter roller.
 2. The constant velocity joint of claim 1, wherein thelength (L) of the concave portion of the guide groove is about the sameas or up to about 12 mm longer than a distance covering each ellipticalcontact area at upper and lower portions of the outer roller.
 3. Theconstant velocity joint of claim 1, wherein the length (L) of theconcave portion of the guide groove is in a range selected from anequation of: L/Rry=0.25-0.6.
 4. The constant velocity joint of claim 1,wherein the guide groove further includes an inner recess area recessedfrom an inner or central area in the concave surface of the groove fordefining a widened space between the guide groove of the housing and itscorresponding portion of the convex outer roller.
 5. The constantvelocity joint of claim 4, wherein the length (L) of the concave portionof the guide groove defined between the upper recess area and the lowerrecess area is about the same as or up to about 12 mm longer than adistance covering each elliptical contact area at upper and lowerportions of the outer roller.
 6. The constant velocity joint of claim 5,wherein each of upper and lower concave groove portions defined betweenthe upper recess area and the inner recess area and between the innerrecess area and the lower recess area, respectively, has a length (L1)which is about the same or up to about 4 mm longer than a correspondingdimension of the elliptical contact area of the outer roller and thehousing.
 7. The constant velocity joint of claim 6, wherein the lengths(L) and (L1) are selected further in consideration of mechanicalstrength requirements of the outer roller and the housing.